The present invention relates generally to a control application for a HACK&R system. More specifically, the present invention relates to a system and method for start-up control of a HVAC&R system.
To minimize energy costs, a structure having a heating, ventilation, air conditioning and refrigeration (HVAC&R) or air treatment system for achieving climate control uses temperature settings that are initiated at HVAC times. For example, in warmer weather, the temperature setting for the structure is set at a higher level during unoccupied hours, and set at a lower level during occupied hours. This lower level temperature setting is an occupied set point or occupied setpoint temperature. It is desirable for the HVAC&R or air treatment system to achieve the occupied setpoint temperature at the start of the time period or setpoint time corresponding to the occupied hours, typically the start of a work shift. To accomplish this, the HVAC&R system must be initiated with sufficient time prior to the setpoint time to allow the HVAC&R system to cool the structure to the desired setpoint temperature, typically referred to as the recovery time. However, initiating the HVAC&R system too far in advance of the start of the setpoint time causes the HVAC&R system to reach the setpoint temperature before the setpoint time, thus wasting energy. Conversely, initiating the HVAC&R system too close to the setpoint time causes the HVAC&R system to achieve the setpoint temperature after the setpoint time has passed, subjecting the occupants in the structure to temperature settings that are outside their comfort level until the setpoint temperature is achieved.
One solution to this problem, U.S. Pat. No. 4,522,336 describes a start/stop controller for controlling an air treatment apparatus at a reduced energy consuming level during periods of non-occupancy of a building and for energizing the air treatment apparatus for occupancy so that the building is comfortable for occupancy. An adjustment time is calculated by taking the difference between the comfort temperature and the setback temperature, and then dividing this temperature difference by the rate of temperature change achieved by the air treatment apparatus. The rate of temperature change is obtained by calculating the temperature difference by the change in time. However, the controller of U.S. Pat. No. 4,522,336 is not adaptive, i.e., it does not take into account variations in the building, control system, or day-to-day differences in outside ambient temperature, and requires application of an arbitrary adjustment factor if the adjustment time falls outside a threshold range. One drawback of this technique is that the arbitrary adjustment factor, as disclosed, can act to increase the time differential between the time the setpoint temperature should be reached and the time the setpoint temperature is actually reached, providing inconsistent climate control inside the building.
What is needed is an adaptable startup control for use with HVAC&R systems that is simple to operate which can provide an optimized startup time for consistently achieving an occupied setpoint temperature at a daily predetermined setpoint time.